(1) Field of the Invention
This invention relates to a multicast communication apparatus and method with network routing, and more particularly to a data mixing method and apparatus using dynamic application layer multicast, particularly but not exclusively for use in audio conferencing and video conferencing systems (in particular, “video conferencing” is also called “Audio and Visual (AV) conferencing” or “television (TV) conferencing”.
(2) Description of Related Art
Application Layer Multicasting (ALM) is implemented on top of existing unicast network architecture for multiple nodes connectivity. ALM allows AV packet routing by the members themselves utilizing an overlay network which is formed by the ALM nodes without any additional router configuration, unlike multicast. ALM nodes exchange route information among them to form an overlay network and exchange packets utilizing this overlay network. This provides the flexibility of real-time and delay sensitive AV packet forwarding at application layer by a large number of multicast groups.
ALM can be used, for example, for a large group of audio conferencing sessions where decentralized mixing can be performed by Multi-point Control Unit (MCU) nodes for the participating nodes. These MCU nodes in turn can re-route the mixed content among them on best ALM path for minimal delay to realize a real-time audio conferencing. The ALM path can carry original audio content or partially mixed audio content to achieve minimal delay and load distribution along the MCU node paths. Minimal delay is achieved via best ALM path selection, while load distribution is done via incremental mixing of source audio content by the ALM-MCU node that mixes the audio content and delivers to the next ALM-MCU or another ALM or end audio node.
If MCU node mixes all audio packets without knowing the content or the source of the content, it might cause an audio echo problem since the duplicated audio content from the same source might be received in partially mixed or original form.
In W. Xiaotao, K. D. Krishna, and K. Venkatesh, “Enhancing application-Layer Multicast for P2P Conferencing”, Consumer Communications and Networking Conference, 2007, 4th IEEE, January 2007, pages 986-990, a hybrid ALM-based P2P conferencing architecture that can take advantage of participating peers with different capabilities for an audio conferencing session is described.
This architecture uses a three-step algorithm to construct such a hybrid ALM-based P2P conference. This approach is more scalable than the existing ALM-based P2P conferencing systems. However, this approach does not consider audio loop problem (i.e. audio echo problem) if the same node were to perform mixing and bridging functions.